1. Field of the Invention
The present invention relates to an interference radio wave elimination device and method for eliminating interference radio waves in radio frequency signals in radio communication system or mobile radio and cellular communication systems, and more particularly, it relates to an interference radio wave elimination device and method for preventing the signal in its own channel from degradation caused by interference radio waves transmitted in the adjacent channels or other channels.
2. Description of the Prior Art
For example, in mobile radio communication systems, each system comprises mobile stations as mobile units such as vehicle communication units and small, hand-held, pocketable communication units (hereinafter referred to as "vehicle communication units" and "pocketable communication units", respectively) and base stations that communicate these mobile stations through radio channels. Between the mobile stations and base stations, a frequency-division multiple access (FDMA) method is widely used for radio communication because each of devices using this FDMA method is simple in technique and configuration.
In the following description relating to a conventional mobile radio communication system, it is assumed that mobile stations receive signals transmitted from the base stations through a predetermined frequency channel (or a desired communication channel). In this case, because communication is performed based on FDMA method, there are adjacent channels which are separated from the main communication channel with a constant frequency difference to relative each other. Interference radio waves which interfere with desired radio frequency signals are transmitted to the desired communication channel. When a movable station receives information transmitted from base stations through a frequency channel allocated to this movable station, it happens that the operation of the mobile station is affected by interference radio waves transmitted from adjacent frequency channels. In this interference, the mobile station causes decoding error signals by the interference radio waves from the adjacent frequency channels. In this case, in the conventional communication system such as the mobile radio communication system, the mobile station abandons this frequency channel allocated to this mobile station, and then the mobile station gets other frequency channel where there is a few interference caused by the adjacent frequency channels. That is, the mobile station (or the same cell) solves this problem by performing a hand-off operation in order to escape from the interference radio waves from the adjacent channels.
The following are documents relating to the conventional mobile radio communication system described above:
Japan Laid-open publication number; JP-A-63/177630, and
Japan Laid-open publication number; JP-A-4/284031. The former discloses the technique to detect the magnitude of interference caused from adjacent channels and the latter discloses the technique that the burst synchronous wave of its own station is in synchronism with the burst synchronous wave of interference radio waves.